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Introduction: It is known that several serum markers are useful as a prognostic factor in septic patients. Endotoxin Activity Assay (EAA) is a first reported as a method for detecting endotoxin based on the ability of antigen-antibody complex to prime neutrophils and augmented respiratory burst response. Endotoxin assay (EA) levels were expressed in relative units derived from the integral of the basal (no antibody) and stimulated (4600pg/ml LPS) chemiluminescent response. Several reports have shown that EA levels were significantly increased in septic patients.The most common predisposing causes of ARDS are sepsis, pneumonia and aspiration.The ARDS on the basis of pneumonia include infectious pneumonia with sepsis and noninfectious pneumonia such as interstitial pneumonia and aspiration pneumonitis. Whereas it is clear that the treatment for ARDS caused by infectious pneumonia with sepsis is the administration of the antibiotics, most cases of noninfectious pneumonias seem to respond to the early initiation of systemic corticosteroid.Although it is important to find the cause of ARDS on the basis of pneumonia, there was no report to show that serum biomarkers distinguish between infectious and noninfectious pneumonia.Since radiologic findings in ARDS patients show bilateral parenchymal infiltrates, it is difficult to distinguish the cause of ARDS definitely between infectious and noninfectious pneumonia.

Hypothesis: EAA may be an appropriate method for distinguishing the cause of ARDS between infectious pneumonia with sepsis and noninfectious in serum biomarkers.

Methods: 12 patients, who were fulfilled the diagnostic criteria for ARDS during our ICU stay from Sep.2009 to Aug.2010 and who did not have an organ disorder except for lung, were included. Blood was sampled at the first day fulfilled our criteria for measuring WBC, CRP, Procalcitonin (PCT) and EAA . After the serious search for the cause of ARDS, such as tuberculosis, atypical mycobacteriosis and atypical pneumonia, 6 patients were infectious pneumonia and the other 6 patients were noninfectious. Bacteria were cultured in all 6 patients of infectious pneumonia. There were 4 patients of interstitial pneumonia and 2 patients of chemical pneumonitis by aspiration in noninfectious pneumonia.

Results: There was no significant difference of WBC count, CRP and PCT levels between infectious pneumonia and noninfectious.In contrast, all patients of infectious pneumonia presented >0.40 unit of EA and all patients of noninfectious presented <0.40. Infectious pneumonia showed significantly higher levels of EA compared to noninfectious.

Conclusions: EAA may be an appropriate method for distinguishing the cause of ARDS between infectious pneumonia with sepsis and noninfectious at bed side.